Anticipated global warming may increase the floret sterility of rice (Oryza sativa L.). For selection of genotypes tolerant to high temperatures during the flowering period, it is important to identify morphological traits associated with tolerance to temperature stress. This study investigated the relationship between the length of dehiscence at the basal part of thecae and the viability of pollination in 18 cultivars of rice subjected to a hot-and-humid condition (37/25°C, day/night, >90% relative humidity) for three days at flowering. Control plants were left under the ambient conditions in a semi-cylindrical house covered with cheesecloth (30% shading; temperature range: 24-35°C). The length of basal dehiscence of thecae and the number of pollen grains on the stigmata were examined with a light microscope after flowering. The length strongly correlated with the percentage of florets having more than 80 pollen grains on the stigmata under the ambient condition (r = 0.72, P < 0.001), and with the percentage of florets having more than 20 pollen grains on the stigmata under the hot condition (r = 0.93, P < 0.001). In other words, the length correlated with pollination viability or reliability under both conditions. In addition, basal dehiscence was shorter in the non-japonica-type cultivars than in many of the japonica-type cultivars under both conditions. We concluded that the low pollination viability in the non-japonica-type cultivars is associated with their small basal dehiscence on the thecae, and the length of basal dehiscence can be used as a selection marker of high temperature tolerance.
To predict mulberry (Morus alba L. ‘Shin-ichinose’) vegetative growth, I constructed shoot elongation and leaf appearance models for mulberry grown in field conditions. The shoot elongation rate and leaf appearance rate were decided by the product of growth activity (GA) and potential rates (PR) realized at the maximum GA under a given environmental condition. GA is dimensionless and ranges from 0 to 1. GA and PR of shoot elongation rate were determined by temperature, photoperiod and shoot length, and temperature and shoot length, respectively. GA and PR of leaf appearance rate were determined by photoperiod, and temperature, respectively. Model parameters were estimated by an iterative method using five-year mulberry growth data. The values calculated by both models were similar to the measured values and represented annual fluctuation well. These models also showed good estimation of data, which were not used for determining parameters. Therefore, it seems that these models well represent mulberry vegetative growth response to temperature and photoperiod, and are practical.
The effects of the amount of nitrogen fertilizer on the starch metabolism of rice leaf sheath during the heading period in the japonica rice variety, cv. Nipponbare were compared with those in the indica varieties, cv. Tetep and Johna. The rice plants were grown under a low- (similar to the standard nitrogen level in paddy field) or high-nitrogen condition, and the starch content of the second leaf sheaths below the flag leaf was analyzed from the second leaf stage (growth stage 1) until 21 days after the heading (growth stage 7). The starch content of the plants grown under the high-nitrogen condition at the heading stage (growth stage 4) was lower than that under a low-nitrogen condition in all the varieties. The decrease in the activity of starch branching enzyme (SBE) was considered to be important for the repression of starch accumulation under a high-nitrogen condition. Under the high-nitrogen condition, Nipponbare accumulated more starch in the second leaf sheath than indica varieties at the heading stage. However, the phenomenon could not be accounted for by the activities of AGPase and SBE. Semi-quantitative RT-PCR analysis suggested that the lower activities of SBE in the second leaf sheath under the high-nitrogen condition may be due to, at least in part, the decrease in the expression level of RBE4.
Adaptive changes were studied comparatively in soybean and cotton grown in pots under four irrigation conditions i.e. normal irrigation (equal to the evapotranspiration of the crop), and 50%, 25% and 10% of the normal irrigation. In soybean, the maximum quantum yield of PSII (Fv/Fm) was generally higher while the actual quantum yield of PSII (ΔF/Fm’) and CO2 assimilation rate (AN) were lower than in cotton. The intensity of the decrease in Fv/Fm, ΔF/Fm’ and AN by water-stress treatments was larger in soybean than in cotton. The decrease in ΔF/Fm’ in soybean under water stress was accompanied by a significant increase in non-photochemical quenching (NPQ) and significant decrease in photochemical reflectance index (PRI). Chlorophyll content decreased significantly under severe water stress only in soybean. The increase in leaf temperature (TL) in response to water stress was significantly larger in soybean than in cotton. TL was highly and negatively correlated with Fv/Fm, AN, PRI and ΔF/Fm’ while it was highly and positively correlated with NPQ of both crops. Especially in soybean, the correlations of TL with AN, Fv/Fm and PRI were significant. It was concluded that soybean adapted to water stress by dissipating the excess excitation energy thermally with the down-regulation of PSII activity to protect its photosynthetic apparatus from the photodamaging effect of water stress and high TL. This photoprotective mechanism might be supported by the paraheliotropic leaf movement of the crop. Cotton adapted to water stress by keeping TL lower to protect the photosynthetic apparatus from photodamage. Probably higher transpiration kept TL of the crop lower under drought stress.
A large proportion of soybean flowers abort during development. Pod set is significantly affected by the availability of assimilate and cytokinin in the flowers, but their synergistic effects on pod set remain unclear. The objective of this study was to examine whether pod set at specific nodes of a plant is enhanced by increasing the source-sink ratio and applying cytokinin to the nodes. The source-sink ratio was manipulated by removing floral buds excluding the specific nodes. As the ratio increased, the number of pods per node of control plants increased curvilinearly, reaching a plateau at high source/sink ratios. By contrast, in the cytokinin-applied plants, the number of pods per node increased without the plateau with increasing source/sink ratio, either by increasing the number of flowers or by increasing the pod-set percentage depending on the year. The results indicated that cytokinin plays a promotive role in increasing pod number in the plants with high levels of assimilate availability.
The aim of this study is to characterize the plasticity of root and shoot morphology in rice, the genomic model plant for cereals, using P deficiency as environmental factor causing variability. A phytotron study on Nipponbare (Oryza Sativa L.) seedlings was conducted to analyze the effects of P deficiency on plant organogenesis (tiller and leaf appearance, root apex number) and allometric relationships (root/shoot weight ratio, specific leaf area (SLA) and specific root length (SRL), blade/sheath weight ratio). The results confirmed that the main effect of P deficiency is a reduction of shoot growth for the benefit of the root system. Reduced shoot growth was associated with reduced tiller production, longer phyllochron and reduced leaf elongation rate while final leaf size remained unchanged. The reduced leaf elongation rate might be a primary response to P deficiency and this caused lower phyllochron and tillering by feedback. Allometric parameters such as SLA, SRL, root apex number per unit length and leaf blade/sheath weight ratio remained largely stable under P deficiency. Increased root growth relative to shoot was associated with increased sucrose concentration in roots, and thus possibly resulted from assimilates liberated by shoot growth inhibition. The simple theory of multiple morphological changes resulting from slow leaf expansion under P deficiency requires further experimental confirmation, after which it may serve as a basis for a mechanistic model of rice phenotypic plasticity and certain genotype X environment interactions on morphology.
The phenological development of winter wheat Iwainodaichi seeded early was compared with that of spring wheat Chikugoizumi based on the temperature. In this paper, the developmental phase from the sowing to double ridge is referred to phase 1, that from double ridge to anthesis phase 2 and that from the anthesis to maturity phase 3. The duration of phase 1 in Iwainodaichi was almost constant independent of the mean temperature in this phase, but that in Chikugoizumi decreased as the mean temperature in this phase increased. When seeded early, the duration of phase 1 was obviously longer in Iwainodaichi than in Chikugoizumi since the mean temperature in this phase was higher when seeded early. The duration of phase 2 decreased in both varieties as the mean temperature and photoperiod in this phase increased. When seeded early, phase 2 was shorter in Iwainodaichi than in Chikugoizumi, since the mean temperature was higher and photoperiod longer in this phase in Iwainodaichi than in Chikugoizumi. The duration of phase 3 decreased as the mean temperature in this phase increased in both varieties and was shorter in Iwainodaichi than in Chikugoizumi at the same mean temperature. Consequently, Iwainodaichi reached the double ridge stage later but reached maturity at about the same time as Chikugoizumi when seeded early.
Flooding during germination often inhibits the germination and emergence of soybean [Glycine max (L.) Merr.], but little is known about the mechanisms involved in the tolerance of soybean cultivars to the damage caused by the flooding. The objectives of this study were to characterize the germination responses of soybean cultivars to pre-germination flooding and low oxygen conditions, and to identify possible seed traits responsible for the tolerance. A comparison of germination percentages among 18 cultivars under optimal and flooding conditions for 3 d enabled the identification of two tolerant cultivars (Williams and Peking), and two susceptible cultivars (Nakasennari and Enrei), which were used for further analyses. A comparison of the water absorption speed (WAS) in the following seed forms: embryo only (E), embryo with aleurone layer (E + AL), and intact seed with aleurone layer and seed coat (E + AL + SC) revealed that the aleurone layer provides a barrier to water penetration during the first hour of inundation regardless of cultivar. The intact seeds of a tolerant cultivar, Peking absorbed water more slowly than the other cultivars in the first hour of flooding. When the oxygen concentration in the seed container was reduced to 70 mL L-1 for 3 d, the germination percentage of susceptible cultivars was reduced to approximately 70 % whereas that of tolerant cultivars remained high, indicating that responsiveness to low oxygen could also be responsible for pre-germination flooding tolerance of soybean cultivars.
Here, we propose new improvement targets capable of decreasing loss of the sturdiness of the lower part in the rice plant (Oryza sativa L.), thereby improving lodging resistance. In nine rice cultivars with various plant lengths, we analyzed the factors responsible for sturdiness of the lower part and, thus, for resistance to lodging. The ratio of lodging resistance to sturdiness of the lower part (RLS) was calculated. The difference in pushing resistance between the lower part and the whole plant varied among cultivars. Among the morphological traits, plant length and the weight of the upper part of plant were not correlated with RLS, but the difference between plant length and length from the ground to the ear (DPE), as well as the weight of the lower stem, were positively correlated with RLS. DPE and the weight of the lower stem were not significantly correlated with ear weight. These results suggest that improvements in DPE and in the weight of the lower stem could be primary targets for improving RLS, thus increasing lodging resistance, without affecting yield.
We assumed that allocation of photosynthate is one of the main factors that regulate lateral root development in root systems under water deficit conditions. Six-days-old maize seedlings were exposed to osmotic stress (-0.21 MPa). Then, the sugar content of the 10 mm segment of seminal roots sampled successively along the root axis was examined in relation to the development and elongation of lateral roots at 0, 1 and 2 after the start of the stress treatment. In the basal 0-40 mm region of the seminal root, latenal roots emerged before the stress treatment, but further initiation and elongation of lateral roots in this region was inhibited by the stress treatment. In contrast, in the region more than 40 mm distant from the base of the seminal root, lateral roots emerged after the start of stress treatment and their development was not influenced or was slightly promoted by the stress treatment as compared with the control plant. The concentrations of glucose and sucrose were determined for every 10 mm segment along seminal root axis. The concentrations of glucose and sucrose tended to increase acropetally, and were increased by the stress treatment, especially in the apical 50-mm portions in both roots sampled after 1 day and 2 days of the stress treatment. On these root portions, while lateral roots had not yet developed when the root was sampled, lateral roots were initiated and they elongated one or two days later. These facts suggest that the accumulation of glucose and sucrose promoted lateral root development, and as a result, canceled the inhibitory effects of stress treatment, and thereby sustained lateral root development under osmotic stress conditions.
Five gibberellins in the early-13-hydroxylation pathway (GA53, GA44, GA19, GA20 and GA1), and six gibberellins in the non-13-hydroxylation pathway (GA12, GA15, GA24, GA9, GA36 and GA4), were detected in the bulbils of Chinese yam. This indicated the presence of two gibberellin biosynthetic pathways in bulbils. The total endogenous gibberellins were dramatically increased in enlarged bulbils. The endogenous level of bioactive GA4 was always higher than that of GA1. A rapid increase in endogenous gibberellins including bioactive GA4 was observed during a 30-day storage period. These results show that gibberellins are closely related to bulbil enlargement and dormancy in Chinese yam plants. However, further research is needed for better understanding of the fluctuation of gibberellin levels in bulbils of Chinese yam during storage.
Anatomical observations were conducted to clarify some characteristics of the crown root primordia (CRP) formation in wheat stems. Unelongated portions of main stems were sampled from the plant at 3.2 and 7.2 plant age in leaf number, which were adopted as indexes because of the similarity to rice plants. Then, serial cross sections were made to investigate the position of CRP in the unelongated stem taking into consideration the running of vascular bundles in the stem. CRP were formed just outside tissues of the peripheral cylinder of longitudinal vascular bundles. The positions of CRP were not successive along the stem axis. They showed no definite relation to the running of vascular bundles. Diameters of CRP at the upper portion of the stems were larger than those at the lower portion. The positions of CRP along the stem axis were not distinguishable into nodal and internodal position. CRP and emerged CRs were not classified by the well-known ‘nodal root’ or ‘shoot unit root’, or the ‘unit’, which have been applied recently to rice plants. Further studies are necessary to clarify the factors controlling CRP formation anatomically and quantitatively.
High temperatures limit wheat (Triticum aestivum L.) production in many areas around the world. Soil temperatures near the root zone could be as high as the air temperature during wheat grain filling. The objectives of this study were to investigate the effects of high soil temperature on grain yield and related traits of wheat genotypes and to examine their differential responses. Three genotypes, Imam, Fang and Siete Cerros were grown under three temperature conditions in the daytime during grain-filling period: (i) normal air temperature/normal soil temperature (26/26°C), (ii) normal air temperature/high soil temperature (26/38°C) and (iii) high air temperature/high soil temperature (38/38°C). The night temperature was 18/18°C in all treatments. Temperatures during the daytime were increased at a rate of 4°C hr-1 from 18°C to the designated temperature, which was kept for at least 4 hr around noon. The 26/38°C and 38/38°C treatments significantly decreased the chlorophyll content (SPAD) of flag leaves, grain-filling duration, and increased carbohydrate remobilization or loss from the stem and the root, but with varying degrees among genotypes. Grain yield, biomass, grain weight, grains number spike-1 and harvest index at the 38/38°C treatment were significantly lower than at the other two treatments. In Imam, the grain yield was lower at 26/38°C than at 26/26°C, while in Siete Cerros the grain yield, grain weight, grain number spike-1 and harvest index were lower at the 38/38°C treatment than at the other two treatments. These results indicated that high temperature of soil alone (26/38°C) or high temperature of both air and soil (38/38°C) decreased the chlorophyll content and grain-filling duration, and increased carbohydrate remobilization. Genotypic differences in the responses to high soil temperature (26/38°C) and high air/soil temperature (38/38°C) were also observed.
In rice, genetic variation in “phyllochron”(the time interval between the appearance of successive leaves) affects many aspects of shoot system development. The objective of our study was to identify quantitative trait loci (QTLs) that control phyllochron in a Lemont (japonica)×IR36 (indica) F2 population. Composite interval mapping detected four phyllochron QTLs located on chromosomes 1, 2, 9 and 11. Individually, these QTLs accounted for 8-14% of the phenotypic variation, indicating that phyllochron is controlled by multiple QTLs rather than by a major gene system. At these QTLs, the presence of a Lemont allele increased phyllochron. The only exception was for the QTL on chromosome 9, where the Lemont allele decreased phyllochron. Based on the synteny between rice and maize genomes, the ortholog of the maize terminal ear 1 gene was considered a candidate gene for the QTL on chromosome 1.
To clarify the characteristics of aigamo duck feces as fertilizer, we analyzed the inorganic components of aigamo duck feces, and examined the correlation of the amount of ammonium nitrogen in soil with the growth and yield of rice, when aigamo duck feces were applied. One gram of air-dried feces contained 26.6mg of total nitrogen. The amount of total nitrogen excreted in feces increased in the period from late June to early July, and remained at the range of about 0.5 g per day after early July. When aigamo duck feces were applied without basal fertilizer, ammonium nitrogen in the soil increased during the late growth stage of rice, but the yield and protein content of brown rice were not. This suggests that the amount of nitrogen supplied from the feces of aigamo ducks is a minor part of nitrogen taken up by rice. It is probably difficult to obtain a sufficient yield of brown rice in the aigamo duck farming system, without nutritional nitrogen supply.
Drainage after sowing promotes plant growth and enhances seedling establishment in rice direct-sown into puddled and leveled soil. We studied the effect of drainage on seedling growth and on dry weight of the plant parts. We also examined carbohydrate, chlorophyll, and protein content of the seedlings grown under flooded and drained conditions to see which factors control plant growth during seedling establishment. Drainage for 10 days after sowing enhanced root elongation but inhibited shoot growth until seedlings emerged above ground. Drainage promoted leaf development and shoot elongation after seedlings emerged but affected root growth only slightly at this stage. Although the dry weight of grain decreased and that of shoot and root increased more rapidly in the drained plot than in the flooded one, the utilization efficiency of grain reserve for shoot and root growth was similar in both plots. Growth analysis indicated that the difference in growth rates between the drained and flooded plots was attributable to the amount of carbohydrates supplied from grain reserve until seedlings emerged, but to the photosynthate after seedlings emerged. Sugar contents of shoot and root in the drainage plot were rather lower than those in the flooded plot as seedlings emerged. In contrast, chlorophyll and protein contents of shoot in the drained plot were markedly higher than those in the flooded one after seedlings emerged. These results suggest that drainage promotes leaf development, increases chlorophyll and protein contents of shoot, accelerates photosynthesis, and enhances dry-matter production after seedlings emerged.